Lewis-Randall and McMillan-Mayer description levels

1 Lewis-Randall and McMillan-Mayer description levels 

In contrast to Pitzer s work, which is given in molalities (Lewis-Randall theory (LR)), the MSA naturally expresses thermodynamic quantities in terms of concentrations, in the framework of the McMillan-Mayer (MM) theory of solutions [33]. Thus, the data have to be converted from Lewis-Randall to McMillan-Mayer scale for adjusting the model to experiment. The basic ingredients of the LR-to-MM conversion have been given [34] and recently an approximate simple conversion has been tested [35]. The great advantage of this transformation is that it keeps the 

It must be underlined that this conversion should be performed in any study using the primitive MSA because, in this framework, the thermodynamic excess functions are calculated at the MM level. The MM framework is characterized by two features the solvent is regarded as a continuum which manifests itself through its permittivity, and the thermodynamic properties are calculated at constant solvent chemical potential. Although the effect of the conversion is negligible at relatively low concentrations it becomes significant as concentration is increased, typically above 1-2 mol/kg [35]. 

For comparison with experiment the quantities are calculated at the MM level as the sum of the electric (MSA) and hard sphere contributions 

The following assumptions have been made [28, 36] about the ion size variation and the permittivity. The anion size was kept constant (equal to its crystallographic value for simple anions or it was adjusted in the case of complex anions) and the diameter of the cation and were chosen as linear functions of the concentration. 

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